Melting of a deep subcontinental lithospheric mantle during the - - PowerPoint PPT Presentation

Sara Mana

smana@salemstate.edu

Melting of a deep subcontinental lithospheric mantle during the early stages of rifting

Mana et al. JGS 2015

Modified from GeoMapApp after Chorowicz 2005 Plate borders and velocity vectors as in Stamps et al. 2008

Continental Rifting Extensional Setting

East African Rift System (EAR)

TECTONIC MODEL GEOLOGICAL SETTING TEMPORAL EVOLUTION SOURCE CHARACTERIZATION RELEVANCE

Afar Plume Kenya Plume

Nelson et al. 2012

Mantle Plume(s) ?

e.g. Ebinger & Sleep 1998; George et al. 1998; Nyblade et

• al. 2000; Lin et al. 2005; Furman et al. 2006; Pik et al. 2006,

Rogers et al. 2006; Chang & Van der Lee 2011

North Tanzanian Divergence Zone

Modified from GeoMapApp – Rift Escarpment age from MacIntyre et al. 1974

?

North Tanzanian Divergence zone (NTD)

Active since 5.8 Ma Mana et al. 2012

TECTONIC MODEL GEOLOGICAL SETTING TEMPORAL EVOLUTION RELEVANCE SOURCE CHARACTERIZATION

NTD Samples Distribution

Ages from: Evans et al. 1971; Fairhead et al. 1972; Isaac et al. 1974; MacIntyre et al. 1974; Hay et al. 1976; Wilkinson et al. 1986; Mollel et al. 2008-2011; Nonnotte et al. 2008; Mana et al. 2012; Sherrod et al. 2013; Mana et al. 2015 TECTONIC MODEL GEOLOGICAL SETTING TEMPORAL EVOLUTION RELEVANCE SOURCE CHARACTERIZATION

Ages from: Isaac et al. 1974; Wilkinson et al. 1986; Mollel et al. 2008-2011; Nonnotte et al. 2008; Mana et al. 2012; Sherrod et al. 2013; Mana et al. 2015

Stages of Magmatic Activity

Material Failure Forecast Method Cornelius & Voight (1995)

Precursory phenomena = volcanic eruption Accelerating volcanism = onset of rifting

Quiescence periods MacIntyre et al. 1974

Activity was episodic

TECTONIC MODEL GEOLOGICAL SETTING TEMPORAL EVOLUTION RELEVANCE SOURCE CHARACTERIZATION

Rifting 1.2-2 Ma

Two main volcanic lineages

Ages from: Isaac et al. 1974; Wilkinson et al. 1986; Mollel et al. 2008-2011; Nonnotte et al. 2008; Mana et al. 2012; Sherrod et al. 2013; Mana et al. 2015

View from north to south

36°E 2°S30’ 37°E 3°S 0 20

New Chronological Framework

TECTONIC MODEL GEOLOGICAL SETTING TEMPORAL EVOLUTION RELEVANCE

Two pulses of enhanced magmatism

SOURCE CHARACTERIZATION

Synrift Major Elements Variation

Empty symbols represent undated samples – Mana et al. 2015; Paslick et al. 1995-96

alkali basalt to trachyte magma series 2.6-1.8 Ma basanite to phonolite magma series

TECTONIC MODEL GEOLOGICAL SETTING TEMPORAL EVOLUTION RELEVANCE SOURCE CHARACTERIZATION

Trace Elements Variations

MgO > 6 wt%

Normalized using Sun & McDonough 1989 e.g. Williams 1969; Paslick et al.1995; Hayes 2004; Mollel et al. 2008; Nonnotte et al. 2011; Mana et al. 2012; Mana et al. 2015 TECTONIC MODEL GEOLOGICAL SETTING TEMPORAL EVOLUTION RELEVANCE SOURCE CHARACTERIZATION

Phlogopite Amphibole

LaTourette et al. 1995

Partitioning of large-ion lithophile elements (LILE)

Hydrous Phases: Phlogopite vs Amphibole

TECTONIC MODEL GEOLOGICAL SETTING TEMPORAL EVOLUTION RELEVANCE SOURCE CHARACTERIZATION

Evidence for a Metasomatized Source

36°E 2°S30’ 37°E 3°S

Ba/Rb >11 AMPHIBOLE

Amphibole is present ubiquitously during the evolution of the NTD volcanism

Sun & McDonough 1989

0 20

Garnet + Amphibole as residual phases in the source Hydrous phases = METASOMATIZED SUB-CONTINENTAL LITHOSPHERIC MANTLE

TECTONIC MODEL GEOLOGICAL SETTING TEMPORAL EVOLUTION RELEVANCE SOURCE CHARACTERIZATION

Partial Melting Model

Normalized using Sun & McDonough 1989

Higher degree of partial melting Increasing Garnet % Increasing Amphibole (3 vs 9 %)

TECTONIC MODEL GEOLOGICAL SETTING TEMPORAL EVOLUTION RELEVANCE SOURCE CHARACTERIZATION

MgO > 6 wt% Ol & Cpx corrected

Variation in GARNET content through time = DEPTH ???

Normalized using Sun & McDonough 1989

Melting in the Garnet stability zone

TECTONIC MODEL GEOLOGICAL SETTING TEMPORAL EVOLUTION RELEVANCE

Partial Melting Model

SOURCE CHARACTERIZATION

Spinel-Garnet transition from Wang et al. 2002

P (Gpa) from algorithm developed by Haase 1996 after correcting SiO2 for fractional crystallization

Depth of Melting

Increasing Depth

TECTONIC MODEL GEOLOGICAL SETTING TEMPORAL EVOLUTION RELEVANCE SOURCE CHARACTERIZATION

Sr-Nd and Pb Isotopic Signature

NHRL (Hart 1984); EACL (Bell & Simonetti 2010); C (Hanan & Graham 1996); Afar Plume (Furman et al. 2006) and ref. therein; Kenya Plume (Aulbach et al. 2011); Kerimasi (Kalt et al. 1997); Oldoinyo Lengai (Bell & Simonetti 1996; Bell & Tilton 2001) TECTONIC MODEL GEOLOGICAL SETTING TEMPORAL EVOLUTION RELEVANCE SOURCE CHARACTERIZATION

Upper mantle low-velocity from 3-D shear wave velocity model presented by Adams et al. (2012)

Plume Related Fluids Layered Lithosphere

Stage 1 and 4 - Melting of Amphibole Rich Veins Stage 2 and 3 - Contributions from hydrous veins was drowned out by melting of a different source component

Two Proposed Tectonic Models

TECTONIC MODEL GEOLOGICAL SETTING TEMPORAL EVOLUTION RELEVANCE SOURCE CHARACTERIZATION

West Turkana Basin

• unique intra-domal region
• evidence for the earliest

phases of both magmatism and extension co-occur

• opportunity to track magma

evolution throughout the history of the basin and constrain plume- lithosphere interactions

TECTONIC MODEL GEOLOGICAL SETTING TEMPORAL EVOLUTION RELEVANCE SOURCE CHARACTERIZATION EAR map modified from Ebinger and Scholz, 2011

Preliminary data…

TECTONIC MODEL GEOLOGICAL SETTING TEMPORAL EVOLUTION RELEVANCE SOURCE CHARACTERIZATION

…Come to see my poster

Thank you!

Sara Mana

smana@salemstate.edu

Oldoinyo Lengai 2010

Collaborators: Merry Cai – LDEO, Columbia University Steve Goldstein – LDEO, Columbia University Sid Hemming – LDEO, Columbia University Cat Beck – Hamilton College Tanya Furman – Penn State University Carl Swisher – Rutgers University Craig Feibel – Rutgers University